Based on the prior art known in the industrial automation market, Ethernet has become a standard choice for digital communication between various pieces of communication hardware. However, very few choices exist for Ethernet-based communication in hazardous areas. One known prior art solution involves the use of a specialized copper cable and connector combination. Another prior art solution involves using fiber optic cables. Both of the above-mentioned prior art solutions suffer from many drawbacks, one of which is the cost of implementing such solutions. Both the above-mentioned prior art solutions are expensive and severely limit the ease of use and maintenance in the field.
For the electrical signals that are not I.S. in hazardous area, the wiring regulations are very stringent and permits very specialized cables often requiring armor (for physical protection against cable cuts) and specialized methods of cable entry and termination. In case of connectors for easy connection mechanism, the connectors must meet the explosion-proof (or flame-proof) requirements. These specialized connectors are not offered for wide range of applications and are expensive.
The fiber (optical link) does not have any electrical energy hence are easily acceptable in hazardous area. The fiber cables are delicate hence easy to break and very difficult to repair in the field. In many industrial applications the fiber cables require special jacket because of environmental conditions and this makes them expensive. In applications where the equipment is permanently mounted, the fiber connectors are not necessary. But in the application where equipments are frequently moved, the connectors are desired. These connectors are expensive and are prone to malfunction due to dust, and are, hence, difficult to maintain.
Since the fiber optic solution is cost-prohibitive and the non-I.S. copper cable and connector solution is not ideal, there is a need for an inexpensive I.S. Ethernet solution. Some of the major benefits of I.S. Ethernet are: (1) industry standard (2) use of standard cable and connector that is widely available at a very cheap cost because the design is I.S. and (3) ability to hot-plug the network. This would reduce that operating cost in the field dramatically and make it user friendly for installation, maintenance, etc.
The serial link is a common method of communication in industrial automation world. There are several advantages of using the serial communication. Some of these are: ease of implementation, lower cost of cabling, very common, hence, ease of finding the alternate and compatible devices etc. Some of the major benefits in the Hazardous area are (1) the ability to make the design Intrinsically Safe due to reduced number of channels (as compared to parallel devices), and (2) the lower cost of implementation for devices, cables and installation.
However, the industrial automation world is moving towards Ethernet as a standard method of communication. This is mainly driven by need for higher communication bandwidth (10 MBPS or greater) than what other serial protocols could provide (typically 1 MBPS or lower). In addition, Ethernet provides users an industrial network that has a lower cost of ownership with improved adaptability for their changing business needs. This, combined with widespread availability and market familiarity, continues to drive Ethernet's use in industrial automation applications for a broad range of industries. Now the Ethernet is widely offered in PLCs as well as devices.
In certain industries, the devices must meet the Intrinsically Safe requirements. The I.S designs are low voltage, low current and has limited power, capacitance and inductance such that even in fault conditions the energy is not sufficient to cause an explosion.
So far, there is no solution available that offers the I.S. Ethernet. One of the inherent problem in I.S. design is the speed as the I.S. design requires putting fuse, Zeners (or diodes) and resistor to limit the voltage and current under fault conditions. These components act like Resistor-Capacitor circuit that distorts frequency characterization of the high speed signals preventing high-speed communication.
The following references provide for a general teaching with regard to communications in hazardous areas, but they fail to provide for the claimed invention's robust method and system of an intrinsically safe Ethernet circuit arrangement that is cost-effective.
The patent to Kessler et al. (U.S. Pat. No. 6,154,683), assigned to Rockwell Technologies, LLC, provides for a Low Voltage Industrial Control System Providing Intrinsically Safe Operation. Hazardous area 20 is provided with intrinsically safe I/O rack 24′, including communications module 30′, which provides high speed serial data communication between control points 36 in the hazardous area and control terminal 22 located outside of the hazardous area over serial link 28′ through penetration circuit 34 to serial link 28 located outside of the hazardous area. Kessler et al. mention the use of a high-speed serial bus and fails to address bandwidth limitations. Also, the general purpose serial link in the industrial control world has a different meaning than Ethernet. Ethernet is not viewed as a serial link due to tight timing requirements.
The patent application publication to Vazach et al. (2005/0024160 A1) provides for an In-Line Passive Barrier for Intrinsically Safe Communication Network. Network barrier 20 is mounted on DIN rail 21 along with communication module 16 of a standard high speed serial network 18, such as Ethernet, and the two are connected by cabling. The barrier is also connected by cabling to network card 16′ of intrinsically safe rack 12′ located in hazardous area 17. The intrinsically safe rack includes I/O modules 14 that communicate with controlled equipment 22 located in the hazardous area (see paragraphs 44-46). The barrier mentioned here is for co-axial cable for high-speed serial communication. The invention here is based on standard ethernet communication with twisted pair cables (ex. CAT5, CAT5e, CAT6) cable using standard RJ145 connector.
The patent to Lewis et al. (U.S. Pat. No. 5,712,631), assigned to Halliburton Company, provides for an Intrinsically Safe Data Network. Provided is a boundary crossing connector, which includes one or more intrinsic safety barriers, that connects a communication interface means located inside a hazardous zone to external processing means. In this patent, it should be noted that the Data Network corresponds to an RS-485 interface (not Ethernet), the implementation is of which is very different than Ethernet.
Whatever the precise merits, features, and advantages of the above cited references, none of them achieves or fulfills the purposes of the present invention.